The present invention relates to stable, particle-filled, organic resin systems wherein, were it not for the use of pacifying reactants and procedures disclosed in this invention, particle-borne contamination would (a) destabilize sensitive resin-binder systems and (b) deleteriously effect good ohmic contact between particles of electroconductive fillers which impart electroconductivity to the systems.
The work of earlier investigators includes a number of methods for assuring processability of polymer compositions which include large quantities of fillers such as electroconductive metal particles. One method has been to segregate the metal particle in a first part of an organic resin binder system which is relatively no-reactive with the metal product and combine the various parts of the binder system just before use. Also, the combination may be made when low storage temperature facilities are available to assure the required processability of the combined system. In other circumstances, the manufacturer, or user of such systems used some chemical-washing technique to remove contamination on powders to optimize their performance. While considerable attention has been given to the effect of filler contamination on the stability of organic binder system, it has also been noted that some polymeric binder systems may themselves contain reactive groups which react unfavorably with metal particles, e.g. undesirably contributing to undesirable chemical coating the surfaces with polymer, oxides, and or other chemicals and, thereby, reducing the electroconductive properties of a mass of such particles in coatings or articles using the polymeric binder system. This reaction may be with the metal itself, but often it is the particle-carried contaminants such as lubricants and the like which are found on most commercially-available metal flakes and many other metal powders.
Thus it has remained a problem in the prior art to provide storable, one-component, compositions which are highly-filled with electroconductive particles. It is a particular problem to provide particles which can be used in a broad-range of filled, organic, binder-systems without fear of excessive deterioration of electrical properties of the systems. A companion problem has been deterioration of the polymer system itself caused by the metal powder or metal-borne contaminants. Contamination caused by the metal powder may result in gelling of the composition rendering the composition useless.
The present inventor has addressed himself to these problems.
It is also noted that tetravalent tin compounds including mercaptides have long been used to provide lifetime heat stabilization for polyvinyl chloride polymer systems. See, for example, Modern Plastics Encyclopedia, 1981-1982 (McGraw-Hill; New York, N.Y.) Pages 200-202.
It is noted that the above discussion of the prior art is necessarily made with knowledge of the present invention. Applicant specifically denies that all the various factors discussed were in fact related one to the other by those skilled in the art at the time the present invention was made.